This invention relates to tubular medical prostheses to be used inside the body.
Medical prostheses, such as stents, are placed within the body to treat a body lumen that has been occluded, for example, by a tumor. The medical prostheses may be formed of wire configured into a tube and are usually delivered into the body lumen using a catheter. The catheter carries the prosthesis in a reduced-size form to the desired site. When the desired location is reached, the prothesis is released from the catheter and expanded so that it engages the lumen wall.
A self-expanding prosthesis is made of highly elastic materials. It is held in a compressed condition during delivery to this site by, for example, a sheath. Upon reaching the desired site, the sheath constraining the prosthesis is pulled proximally, while the prosthesis is held in the desired position, enabling the prosthesis to self-expand by its own elastic restoring force.
A non-self-expanding prosthesis is made of less elastic, plastically deformable materials. It is positioned over a mechanical expander, such as a balloon, which can be inflated to force the prosthesis radially outward once the desired site is reached.
In a first aspect, the invention features an implantable medical prosthesis. The prosthesis is a tube-form body with a body wall structure having a geometric pattern of cells defined by a series of elongate strands extending to regions of intersection. The prosthesis has interlocking joints at the regions of intersection formed by a portion of at least one of the strands being helically wrapped about a portion of another strand.
Embodiments may include one or more of the following. Portions of the strands are helically wrapped about each other. The interlocking joints are constructed such that the axis of the helically wrapped portion is oriented generally circumferentially with respect to the tube-form body. The interlocking joints are also constructed such that the helically wrapped portions of the strands can move relative to each other when the prosthesis is subject to varying radial compressive forces while still maintaining the cell structure. The strands are helically wrapped through a single 360 degree rotation and are metal wires composed of a Nickel-Titanium alloy. The prosthesis is self-expanding. The prosthesis includes a sleeve-type covering. The prosthesis is constructed for use in the biliary system and has a fully expanded diameter of about 10 mm, and is compressible to a diameter of about 9 French without plastic deformation. The prosthesis is constructed to plastically deform during expansion. The prosthesis is also constructed of a shape memory material to enable expansion in response to a temperature change. The prosthesis includes a drug-delivery layer carried by the wall structure. The prosthesis is constructed as a temporary stent, such that an end of the stent is connected to a drawing member that permits withdrawing the stent after deployment.
In another aspect, the invention features a method for creating a tubular medical prosthesis by providing a mandrel of size selected to substantially correspond to the diameter of the stent, the mandrel being adapted to removably receive a pattern of radially extending pegs, by providing elastic wire strands, and forming the prosthesis by fixing the strands at one end corresponding to an end of the prosthesis, drawing the adjacent strands to an adjacent, axially spaced peg, joining the strands such that the peg maintains the drawn portions of the strands in tension, repeating the drawing and joining to form a tubular member of desired length, and removing the prosthesis from the mandrel by expansion.
In embodiments, the method may also include one or more of the following. The method may include providing a mandrel formed of a heat-resistant material, and heat-treating the mandrel and the prosthesis prior to removing the prosthesis from the mandrel. The method may include fixing the ends of the strands corresponding to the other end of the prosthesis, after heat-treating said prosthesis. The method may include joining the strands by helically wrapping the strands about each other. The method may include providing a mandrel adapted to receive the pegs in a diagonal pattern extending axially along the length of the mandrel. The method may also include providing metal wire strands formed of a nickel-titanium alloy.
In another aspect, the invention features a system. for treating an occluded body lumen. The system includes a prosthesis having a tube-form body with a body wall structure having a geometric pattern of cells defined by a series of elongate strands extending to regions of intersection, and interlocking joints at the regions of intersection formed by portions of the strands that are helically wrapped about each other. The system also includes a delivery catheter constructed to receive the prosthesis in a compact state for delivery through the body to a desired site in the body lumen, and to allow expansion of the prosthesis to larger diameters for engaging the body lumen at the desired site. The delivery catheter includes a sheath constructed to maintain the prosthesis in compact form during the delivery. The interlocking joints of the prosthesis are constructed such that the axes of the helices of the helically wrapped portions of the strands are oriented generally circumferentially with respect to the tube-form body. The interlocking joints are also constructed such that the helically wrapped portions of the strands can move relative to each other when the prosthesis is subject to varying radial compressive force while still maintaining said cell structure. The strands forming the interlocking joints are helically wrapped through a single 360 degree rotation and are metal wires composed of an Nickel-Titanium alloy. The system may be constructed for use in the biliary system such that the prosthesis has a fully expanded diameter of about 10 mm, and be compressible to a diameter of about 9 French, without plastic deformation.
In another aspect, the invention features a method for treating a body lumen. The method may include using a prosthesis having a tube-form body with a body wall structure having a geometric pattern of cells defined by a series of elongate strands extending to regions of intersection, and interlocking joints at the regions of intersection formed by portions of the strands that are helically wrapped about each other, using a delivery catheter constructed to receive the prosthesis in a compact state for delivery through the body to a desired site in the body lumen and to allow expansion of the prosthesis to larger diameters for engaging the body lumen at the desired site, delivering the prosthesis to the site on the catheter, and releasing the prosthesis at the site.
In embodiments, the method may also include treating a body lumen having a highly torturous bend, by providing and delivering the prosthesis to the bend. The bend may approach 80xc2x0-90xc2x0.
Prostheses of the invention, such as stents, have an advantageous combination of properties. The stents can exert large radial outward forces that can open or maintain a lumen that has been occluded by disease. Yet the stents can also be compacted to a relatively small diameter so that they can be delivered into narrow lumens. The stent cell structure uniformly collapses in a preferential orientation permitting the stent to be compressed into a relatively small diameter. These properties are enabled by the stent construction. The cell structure of the stent wall contributes to the large radial forces since adjacent cells reinforce each other and allow force transmission along the length of the stent. Interlocking joints, preferably arranged with joint axes extended in circumferential fashion, maintain the cell structure at all levels of expansion and compression. The joints allow an elastic pivoting of the wires at the joint. The joints also distribute stresses along the lengths of the wire portions forming the joints and adjust slightly by loosening and tightening. The joints are highly resistant to failure by shear forces, even when repeatedly compressed and expanded. The stents are effective in highly tortuous passageways since they resist buckling when bent to extreme radii, thus maintaining an open path through the stent. Yet, the stent is relatively flexible such that it bends easily as it is being delivered in a catheter into the tortuous passageway. The stents also exhibit only a small difference in axial length between compressed and expanded states. Moreover, the prostheses can be manufactured readily and in a cost-effective manner.
Other features and advantages follow.